Alphanumeric keyboard

ABSTRACT

A key-operated actuating mechanism for an alphanumeric keyboard in which the key bears through a stem on one side of a flexible electrically conductive tongue which has one end fixed. A fulcrum is mounted proximate the other side of the tongue between the key and the free end for causing the tongue to bow when the key is depressed. The depression of the key causes the free end of the tongue to swing up and to break its electrical contact with a first contact and to establish electrical contact with a second contact. This in turn causes a source of electrical potential to be differently connected to winding on a magnetic core having a square hysteresis loop and thereby switches the core to the opposite state. An output signal is thereby generated in output windings on the core, the output signal being so coded as to identify the key struck.

United States Patent [72] lnventor Alfredo Olivei Turin, Italy [21] Appl. No. 795,005

[22] Filed Jan. 29, 1969 [45] Patented Aug. 24, 1971 [73] Assignee Ing C. Olivetti & C., S.p.A.

lvrea, Italy {32] Priority Feb. 13, 1968 [33] Italy [54] ALPHANUMERIC KEYBOARD 7 Claims, 7 Drawing Figs.

[52] U.S.Cl 178/17 C, 197/98, 235/145 [51] Int. Cl H041 15/06 [50] Field of Search 235/145,

146; 179/90 BB, 90 BD, 90 K; 178/17 A, 17 C, 17; 197/98; 200/67 D; 340/365 [5 6] References Cited UNITED STATES PATENTS 3,487,184 12/1969 Arthur 200/67 3,495,236 2/1970 Mathamel 340/365 3,303,290 2/1967 Suloway 179/90 3,255,639 6/1966 Russell 74/96 3,040,304 6/1962 Brewster 340/174 2,997,703 8/1961 Powell 340/347 2,904,636 9/1959 McKim.... 179/18 2,849,539 8/1958 Abbott 179/90 2,835,741 5/1958 Vaughan..... 179/90 2,505,605 4/1950 Coaice 200/67 Res.25,235 9/1962 Lee 178/79 Primary Examiner- Kathleen H. Claffy Assistant Examiner-Tom DAmico Attorney-lrons, Birch, Swindler & McKie ABSTRACT: A key-operated actuating mechanism for an alphanumeric keyboard in which the key bears through a stem on one side of a flexible electrically conductive tongue which has one end fixed. A fulcrum is mounted proximate the other side of the tongue between the key and the free end for causing the tongue to bow when the key is depressed. The depression of the key causes the free end of the tongue to swing up and to break its electrical contact with a first contact and to establish electrical contact with a second contact. This in turn causes a source of electrical potential to be differently connected to winding on a magnetic core having a square hysteresis loop and thereby switches the core to the opposite state. An output signal is thereby generated in output windings on the core, the output signal being so coded as to identify the key struck.

PATENTED M1824 I971 3501 5134 SHEET 1 or 4 Fig.1

Fig. 2

INVENTOR. ALFREDO OLIVEI PATENIEU AUG24 |97I SHEET 2, [IF 4 Fig.3

Fig.4

INVENTOR. ALFREDO 0L IVEI PATENTED AUE24I97| 3,601. 534

SHEET 3 OF 4 Fig.6

INVENTOR. ALFREDO OLIVEI PATENTEU AUB24I97| 3. 601,534

sum u u; 4

INVENTOR. ALFREDO OLIVE! ALPHANUMERIC KEYBOARD BACKGROUND OF THE INVENTION The present invention relates to an electronic keyboard for entering data in data priming, transmitting or processing equipment, having coded output signals in parallel on a plurality of lines and with coding obtained by means of ferromagnetic cores. More particularly, the invention relates to a keyboard of the type comprising a set of operating keys actuated by means of a manual mechanical movement and with each of which there is associated a bistable magnetic core which maybe saturated positively or negatively by input wires to produce in parallel on a'plurality of output wires a combination of binary signals representing the character of the corresponding operating key in a given code.

There are essentially two requirements which must be met by an electronic keyboard with an output in code: a) all the keys must operate independently from one another, that is to say if one or more keys are kept depressed it must also be possible to write other characters; b) the risk of superimposition of two characters due to the simultaneous striking of the corresponding keys must be reduced to the minimum so as to avoid the mixing or superimposition on the output lines of the two codes corresponding to the characters struck simultaneously.

In known keyboard, this drawback is obviated by introducing an interlocking or regeneration device, which is very burdensome from the economic point of view.

In the present invention, all interlocking or regeneration devices are dispensed with, since the coding signals have a duration which is much shorter than time of offset which occurs in the so-called simultaneous striking of two keys.

It is necessary to make a number of observations as regards the simultaneousness ofthe striking of two keys.

As the result of a careful statistical investigation, it has been observed that the probability of the occurrence of simultaneousness of the striking of any two keys is almost nil, inasmuch as two keys which are apparently struck simultaneously always show two impacts offset in time and separated by a brief period of time T. The statistical investigation was aimed at establishing the most probable value of the time of offset T in the simultaneous striking of two keys.

It is possible to associate with each time of offset a probability P, which can be interpreted as the relative frequency with which a given time of offset T appears. Graphs have been plotted for given operators in which there appear as abscissae the time of offset T measured with an oscilloscope and as ordinates the relative frequency P with which a given time of offset T appears (FIG. 1).

There is obtained for all operators a bell-shaped or Gaussian curve of the form.

in which I represents a proportionality factor and a the average spread.

The most probable time of offset for all operators is. around ms. It can therefore be concluded that if the duration of the coding signals is less than ten milliseconds, the risks of superimposition of the output signals are extremely small. By choosing a time around one microsecond as the duration of the output signals on the coding lines, the risks of superimposition are reduced to the minimum or almost excluded and all need for interlocking and control devices in the keyboard are avoided. To this end, there is associated with each operating key a magnetic core into which there pass, in addition to the biasing wires and the input wires, also the output wires which supply in a given code the signals representing the character corresponding to the operating key.

The use of mechanical switches of known types, for example microswitches for switching the core requires time of actuation and return which are too long because of the combined movement ofa plurality of mechanical'parts, so that the speed of the electric signals generated is accompanied by a relative slowness of the mechanical operative portion. Therefore, under these conditions, the speed of entry permitted by the keyboard is jeopardized by its mechanical qualities.

OBJECTS AND SUMMARY OF INVENTION It is therefore an object of the present invention to provide means actuated by the operating keys which effect the rapid changeover of saturation of the magnetic cores in such manner that the times of mechanical operation of the changeover are much less than the most probable time of offset of striking and, moreover, are of an order of magnitude next to that of electronic changeover of the cores.

The aforesaid drawbacks are obviated and the aforesaid object is achieved in the keyboard according to the invention, which provides an electronic keyboard comprising a set of manually operable keys, each of which bears on a metal changeover tongue which makes contact with one of two contacts in the unoperated and operated positions respectively of the key and thereby connects biasing wires differently to a voltage source, the biasing wires linking a bistable magnetic core associated with the key in an arrangement such that the core is saturated in its two different senses in the said unoperated and operated positions respectively and induces in output wires linking the core a combination of pulses representing the operated key in a given code.

BRIEF DESCRIPTION OF THE DRAWINGS v The invention will be described in more detail, by way of example, with reference to the accompanying drawings, in which:

FIG. I is a diagram which represents the probability of the time of offset in the striking of two keys operating consecutively;

FIG. 2 shows the time diagrams of the input and output voltages for the magnetic cores used in the present invention;

FIG. 3 shows one embodiment of the working principle of a keyboard embodying the invention;

FIG 4 shows the hysteresis curve of a magnetic core used in the keyboard;

FIG. 5 shows a particular form for the circuit for changing over the bias of the magnetic cores employed in the keyboard;

FIG. 6 shows different waveforms of the output signals produced by the keyboard;

FIG. 7 shows a constructional form of a keyboard embodying the invention.

DETAILED DESCRIPTION changeover in the saturation of the magnetic core occurs and as output on the coding wires there is obtained the coded signal in parallel of a preestablished duration, for example 900 ms, which depends solely on the time necessary for reversing the flux in a core.

Once the bias of the core has been reversed, there will no longer be any signal on the output wires even if the operator continues to keep the key depressed. The aforesaid coding output are therefore free to receive a fresh character code and so on. In this way, the independence of operation of the keys is insured. When a key returns to the inoperative position, with a change from the positive source to the negative source of supply for the input wire to the core, there will be collected at the outputs a signal of opposite sign which will be disregarded or eliminated in conventional manner.

FIG, 2 shown the diagrams of the variation in time of the feed voltage Vi on the input wire to the magnetic core and of the voltage Vu collected as output on the coding wires. The time interval indicated by tpn represents the time necessary for the change from the connection to the positive source to the connection to the negative source (and vice versa), which is mechanical time necessary so that the changeover switch may be brought, from interruption of the contact with the positive pole, to initiate the contact with the negative pole; for good operation of the keyboard from the point of view of the mechanical speed of changeover, this interval must be less than 200 us.

As regards the possibility of the return of a key to the inoperative position coinciding with the movement of another key into the operative position, with consequent cancellation of the signals on one or more output coding wires, since the output signal produced by the return of a key to the inoperative position would cancel the input signal produced by the other key, which is of opposite sign, it can be considered that the same considerations as were discussed with regard to the simultaneousness of striking of two keys are valid.

For the purpose of obtaining good mechanical efficiency of the keyboard as required, the connection between the input wires of the cores and the positive or negative source is insured in the illustrated embodiment by simple ohmic contacts actuated directly by the key.

Referring to FIG. 3, there appears a diagrammatic representation of the contacts a and b of the key 1 and of the changeover tongue 2. In the inoperative position a hump a present at one end 3 of the tongue 2, which is fixed at the other end 4, bears on'the negative contact a. When the key 1 is depressed, the tongue 2 comes to bear on the fulcrum f. This causes the tongue to bow so that the hump a is separated from the negative contact and another hump b present at the end 3 of the tongue 2 is brought into contact with the positive pole b. One of the advantages of this device is that no only do the humps a and b touch the respective contact surfaces a and b, but owing to the effect of the bending of the tongue 2 they are compelled to slide thereon, thereby ensuring better contact and better operation. Moreover, the tongue 2 also serves as a spring for the key. In order to insure the sliding contact on contact a the fulcrum f is slightly spaced from the tongue in the inoperative position of the key.

The operator is able to bear resiliently on a key depressed into the end-of-stroke position or in the inoperative position without any risk of causing a signal on the output channel, since the core is able to supply a fresh signal only when the key has passed into the position opposite to that in which it is when the operator bears resiliently thereon.

It is known that sliding contacts show many fallings-off or drops in voltage, at times down to zero, during the establishment of the contact itself. In the present case, these fallings-off have no effect, because once the core has reversed its saturation it remains in the reversed state as long as the input wire is not placed in contact with the source of opposite sign again.

The circuit of FIG. 3 illustrates the principle of operation for one key, it being understood that for each key there is a circuit identical to that show in the FIGURE, each with its code corresponding to the character represented by the respective operating key.

For simplicity of the drawing, a bistable magnetic core 5 is shown diagrammatically by a thick straight line. A winding on the core is indicated by a short line inclined to the left if the winding is in one sense termed direct and by a short line inclined to the right if the winding is in the inverse sense.

The magnetic core 5, with a rectangular hysteresis loop (FIG. 4), is provided with a winding with an input wire I constituted by a single turn wound in the direct sense, a winding with an input wire N constituted by a single turn wound in the inverse sense and the outgoing or output coding wires indicated by the references C1 to C7, which are wound in the direct sense. For example, there may be provided seven coded outputs for the lower case characters and seven for the upper case characters which can be selected by means of a shift key, so that the operator can write lower or upper case according to his requirements.

The wires land N are made of nickel-chromium.

The wire N is the biasing wire of the core and is connected from the positive pole of the source E through the current limiting resister R to earth and the wires indicated by the references C1 to C7 are the coding wires connected between earth and the respective outputs U1 to U7. The resistance of the circuit through the wire N is larger than that through the wire I (either by use of a high resistance wire or by use of a limiting resistor in series with the wire N) so that the current in the wire N is only a small fraction of that flowing in the wire l.

Each core 5 therefore has a relatively small inverse magnetic biasing field by virtue of the current flowing through the biasing wire N. The biasing field will be regarded as negative. With the key in the position indicated in FIG. 3, each core is also subjected to a relatively large inverse field due to the current flowing through the input wire indicated by the reference I which is connected to the negative pole of the source E through the tongue 2 and the contact a.

FIG. 4 shows the hysteresis curve of a core zero field being represented by point 9. When the key is in the position indicated in FIG. 3, the core is saturated negatively by the combined effects of the currents in the wires I and N and its state is represented by the point 6 in FIG. 4. Assuming that the key is depressed, then the sign of the voltage is reversed and a relatively large forward current now flows through the wire I overcoming the reverse bias. It is well known that in the input wire I there occurs a counterelectromotive force equal to the voltage E applied and the current which is established will be such that these conditions are satisfied.

For each core the counterelectromotive force is equal to df/dt, in which f is the flux and t is the time. Immediately after the voltage is changed from negative to positive, the working point on the hysteresis loop shifts from 6 to 7 and, at the same time, the saturation of the core is reversed, so that there is a change to the point 8 on the hysteresis loop, and the time T necessary for the reversal depends on the total variation 2F of the flux.

In the ideal case, in which df/dt is constant, it follows that 1'=2F/E, in which 1- represents the duration of the pulse which is collected on the coding wires at the outputs U1 to U7 and sent to the feed devices, and E is the applied voltage.

In the practical carrying into effect of the keyboard it is possible to carry out further simplifications. In effect, the two bias sources E and E shown in FIG. 3 can be reduced to a single source with a single sign, for example +E. In fact, referring to FIG. 5, it is observed that, by employing the tongue 2 shown diagrammatically in FIG. 3, a single wire L linked both in direct manner and in inverse manner with the core 5 and a single voltage source E is sufficient to change over each core 5. The wire L has an intermediate point F connected to earth and its ends connected to two contact positions A and B.

Let us assume that the changeover element or switch 2 is closed at B as indicated in FIG. 5. The current i then flows in the direction indicated by the arrow, the respective energization field H is oriented in the manner indicated in FIG. 5 and the core is saturated negatively at the point 6 of FIG. 4. When the connection is brought from B to A, the current i, then flows in the opposite direction to the previous one as indicated by the arrow and, thus, the energization field H 4 also has the opposite direction to the previous one and the same absolute value. The core is consequently saturated positively at the point 8 of FIG. 4. In the changing over from negative saturation (point 6 of FIG. 4) to positive saturation (point 8 of FIG. 4) the changeover signal of the core is collected at the output of the coding wires. The effect of this new arrangement compared with the arrangement hereinafter described is manifested in a variation of the form and amplitude of the changeover signal, as indicated in FIG. 6.

It has been found experimentally that with the use of the relatively small biasing current in line N as shown in FIG. 3, the changeover signal has the form and amplitude shown by curve Q in FIG. 6, while in the simplified arrangement of FIG. 5 the changeover signal has the course indicated by the curve S. In the simplified arrangement, there is a decrease of approximately percent in the amplitude of the voltage of the changeover signal with respect to the optimum arrangement. That is, there is obtained a signal S which is reduced by the effect of the initial bias provided by the wire N in the arrangement illustrated in F IG. 3. FIG. 4 illustrates the hysteresis curve developed preferably by the arrangement of FIG. 3.

In view of the great versatility of the keyboard, the coding of the output signals may be most varied and other lines (for example an eighth line for timing), which may possibly be neces sary for the operation of storage devices for a plurality of characters, may be added to the seven lines for the lower case characters and the seven lines for the upper case characters.

A constructional form of a keyboard according to the invention is shown in FIG. 7. A single wire L which may be of nickel chrome with a diameter of 0.3 mm. is wound in the manner indicated in FIG. 7 on a core 5 to effect the switching of the core. In the inoperative position of the key 1 the tongue 2 closes the circuit by means of the hump a through the contact A, so that the core is saturated negatively. When the key 1 is depressed into the operative position, the contact A is opened and the contact B is closed via the hump b of the tongue 2. The

current then flows in the opposite direction to the previous one and the core 5 switches to positive saturation.

A magnetic amplification of the output signals is effected at the output of the coding channels C1, C2, C3 As indicated in FIG. 7, each line C is connected to the primary P of a transformer which may have a primary of about a hundred turns, while the secondary S may be constituted by about a thousand turns, so that the signal at the output U is amplified 10 times. In parallel with the output U of the secondary S there may be connected a capacitor C of 1000 pF and a diode D which have the function of eliminating disturbances and suppressing the signals of a given sign, for example the negative signals.

The use of a single nickel-chrome wire for biasing purpose enables a distributed load resistance to be obtained for the voltage source.

Referring to FIG. 7, as regards the arrangement of the keys, a plastic plate 9 has through seats 10 in which the keys are simply inserted, the keys being formed in one piece, made of plastic and of parallelepipedal or cylindrical form and having at their base a flange 11 which prevents the keys becoming disengaged from the keyboard once they have been inserted into the plate 9 from below. Each key is moreover extended and bears by means of a stem 12 directly on the changeover tongue 2, which may be made of beryllium bronze with a thickness of around 0.2 mm.

It will be observed that in the inoperative position the stem 12 of the key bends the tongue 2 slightly, so that the lip 11 is always held against the upper plate 9 and the contact A is closed via the hump a of the tongue 2 which bears thereon.

When the key 1 is depressed, the tongue 2 bends and is lowered until it touches the fulcrum f, which is located 0.5 mm. from the tongue when the key is in the inoperative position. From the moment when the tongue touches the fulcrum f and only from this moment, the contact A opens and the key, continuing its stroke, bends the tongue further and the hump b of the tongue at the end 3 continues to rise until it closes the contact B.

When the key is in the pressed position it can work elastically on the spot without the contact B being broken; likewise, it can work elastically on the spot in the inoperative position without the contact A being broken.

Moreover, when the action of manual pressure on the key 1 ceases, the tongue 2 itself restores the key to the inoperative position.

The tongue 2 therefore performs a plurality of duties, that is of contact and springing and return of the key.

The contacts A and B may be formed as plane portions of a printed circuit by suitably metallizing the plates 9 and 13, as shown diagrammatically in FIG. 7. For geometrical reasons, the contact B is situated on a projection 14 of the plate 9, which could be formed at the same time as the plate 9 by moulding.

The changeover tongues 2 may form part of a single metal plate 15 cut so as to comprise as central body from which there extend arms or branches to form the tongues 2. The central body of the plate 15 may be rivetted to a projection 16 of the lower plate 13. The metal plate 15 is then connected to one pole (for example, the positive pole) of the voltage source E, the other pole being grounded.

I claim:

1. An alphanumerical keyboard comprising:

a. a plurality of elastically flexible changeover tongues anchored at one end to a fixed support and movable at the other end,

. a plurality of manually operable keys each of which bears directly on a corresponding tongue,

c. a first and a second contact mounted proximate said other end of said tongue for making electrical contact respectively with one side of said tongue when said key is in an unoperated position and with the other side of said tongue after said key is operated and depressed beyond a predetermined amount,

. said first and second contacts being adapted to be connected to sources of electrical potential having opposite polarities with respect to a point of reference potential,

e. a magnetic core associated with each tongue of said plurality of tongues, said core having two opposite statuses of saturation,

. a first winding on said core connected between said tongue and said point of reference potential through said second contact,

g. a second winding on said core connected between said first contact and said point of reference potential,

. said first and second winding linking the bistable magnetic core in opposed directions so that the core is saturated in two different statuses in the said unoperated and operated positions respectively, and

i. a plurality of output windings linking the core for producing, upon the changing of status of saturation, a combination of output pulses representing the operated key.

2. A keyboard as recited in claim 1 including a metal plate comprising a central body portion anchored to said fixed support and a plurality of resilient flexibly supported arms extending from said central body and wherein said plurality of resilient arms are adapted to serve as said plurality of flexible tongues.

3. A keyboard as recited in claim 2, wherein said first and second contacts are plane portions of a printed circuit.

4. A keyboard as recited in claim 2 including a stem intermediate each of said plurality of tongues and said corresponding key, said tongue operating through said stem to restore said corresponding key to its unoperated position when the key is manually released.

5. Analphanumerical keyboard comprising:

a. a plurality of manually operable keys,

b. a plurality of elastically flexible tongues each fixably mounted at one end and associated with one of said plurality of keys,

c. actuating means coupled to each of said keys, having a rest position and being movably mounted for depressing one side of said associated tongue at a point intermediate the ends when said key is actuated,

. snap means mounted proximate the opposite side of said tongue intermediate said actuating means and the other end of said tongue for causing said other end of said tongue to swing in the opposite direction to said actuating means,

. first and second contact means mounted proximate said other end of said tongue when said actuating means is in its rest position and a second state of contact with said tongue when the key is actuated, respectively,

. plurality of magnetic cores each associated with one of said plurality of tongues each having a pair of opposite stable magnetic states,

g. means for connecting said fixed end of said tongue to one terminal of a voltage source providing a fixed potential with respect to reference potential,

h. first and second biasing wires associated with each of said cores coupled between said first and second contact means and reference potential and linking said core in opposite senses, said wires causing said core to switch to the opposite state when said tongue is in said second state of contact, and

i. a plurality of output winding means on each of said cores for generating an identifying code signal upon the switching of said core.

6. A keyboard as recited in 5, wherein said first and second biasing wires are provided in the form of a single wire having two portions which link said core in opposite senses and including a point intermediate said oppositely linking portions connected to said reference potential, the ends of said biasing wire being connected to said first and second contact means respectively, each of said two portions constituting a distributed load resistance for the voltage source.

7. A keyboard as recited 5, wherein each output wire is connected to a stepup transformer having a capacitor and a diode in parallel with its output for absorbing disturbing signals and suppressing pulses of one sign.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 601 531} Dated Ang a; 2! ]91] Alfredo Olivei.

Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 6, line 70, after "tongue", should read for providing a first state of contact with said tongue Signed and sealed this 24th day of October 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTI'SCHALK Attesting Officer Commissioner of Patents USCOMM-DC 60376-F'69 DRM PO-1050 (10-69) :1 u 5. GOVERNMENT rmurmc OFFICE l9" man-:34. 

1. An alphanumerical keyboard comprising: a. a plurality of elastically flexible changeover tongues anchored at one end to a fixed support and movable at the other end, b. a plurality of manually operable keys each of which bears directly on a corresponding tongue, c. a first and a second contact mounted proximate said other end of said tongue for making electrical contact respectively with one side of said tongue when said key is in an unoperated position and with the other side of said tongue after said key is operated and depressed beyond a predetermined amount, d. said first and second contacts being adapted to be connected to sources of electrical potential having opposite polarities with respect to a point of reference potential, e. a magnetic core associated with each tongue of said plurality of tongues, Said core having two opposite statuses of saturation, f. a first winding on said core connected between said tongue and said point of reference potential through said second contact, g. a second winding on said core connected between said first contact and said point of reference potential, h. said first and second winding linking the bistable magnetic core in opposed directions so that the core is saturated in two different statuses in the said unoperated and operated positions respectively, and i. a plurality of output windings linking the core for producing, upon the changing of status of saturation, a combination of output pulses representing the operated key.
 2. A keyboard as recited in claim 1 including a metal plate comprising a central body portion anchored to said fixed support and a plurality of resilient flexibly supported arms extending from said central body and wherein said plurality of resilient arms are adapted to serve as said plurality of flexible tongues.
 3. A keyboard as recited in claim 2, wherein said first and second contacts are plane portions of a printed circuit.
 4. A keyboard as recited in claim 2 including a stem intermediate each of said plurality of tongues and said corresponding key, said tongue operating through said stem to restore said corresponding key to its unoperated position when the key is manually released.
 5. An alphanumerical keyboard comprising: a. a plurality of manually operable keys, b. a plurality of elastically flexible tongues each fixably mounted at one end and associated with one of said plurality of keys, c. actuating means coupled to each of said keys, having a rest position and being movably mounted for depressing one side of said associated tongue at a point intermediate the ends when said key is actuated, d. snap means mounted proximate the opposite side of said tongue intermediate said actuating means and the other end of said tongue for causing said other end of said tongue to swing in the opposite direction to said actuating means, e. first and second contact means mounted proximate said other end of said tongue when said actuating means is in its rest position and a second state of contact with said tongue when the key is actuated, respectively, f. plurality of magnetic cores each associated with one of said plurality of tongues each having a pair of opposite stable magnetic states, g. means for connecting said fixed end of said tongue to one terminal of a voltage source providing a fixed potential with respect to reference potential, h. first and second biasing wires associated with each of said cores coupled between said first and second contact means and reference potential and linking said core in opposite senses, said wires causing said core to switch to the opposite state when said tongue is in said second state of contact, and i. a plurality of output winding means on each of said cores for generating an identifying code signal upon the switching of said core.
 6. A keyboard as recited in 5, wherein said first and second biasing wires are provided in the form of a single wire having two portions which link said core in opposite senses and including a point intermediate said oppositely linking portions connected to said reference potential, the ends of said biasing wire being connected to said first and second contact means respectively, each of said two portions constituting a distributed load resistance for the voltage source.
 7. A keyboard as recited 5, wherein each output wire is connected to a stepup transformer having a capacitor and a diode in parallel with its output for absorbing disturbing signals and suppressing pulses of one sign. 